Currently i'm working on some NAT traversal code (that allows to computers each behind it's own NAT to communicate with each other). But, surprisingly, i can't find any symmetric NAT's! (it's the most hard case). Anyone knows where can i find one, wither in software or hardware? It seems that windows 'internet connection sharing' is not symmetric :(.

Is it any good guide how to configure simple test NAT on FreeBSD? I have installed FreeBSD 7.2-RELEASE on one of my computers, but adding your string to rc.conf will raise error "nat not found" :)
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Eye of HellAug 27 '09 at 10:53

i would suggest seeing if you can get your hands on a cisco virtual device (example/sample), i know their routers can support Symmetric Nat, so you could build one real quick and see if it works for you in VMs.

Also check VMwares site for other possible appliances that might do this for you.

You can also use something like Dynamips or GUI utility like GNS3 ( gns3.net ) to emulate cisco devices, using IOSes from ISOHunt.com, and connect virtual cisco network to the real one.
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SaveTheRbtzAug 25 '09 at 21:57